The 2.8 earthquake was recorded at 12:35 a.m. Thursday. It was centered about four miles east of the Delta County town, which is surrounded by working coal mines, as well as orchards and wineries.
Bruce Presgrave, a geophysicist with the U.S. Geological Survey, told The Daily Sentinel that it was probably caused by a coal bump or a rock burst.
A coal bump is when a pillar of coal suddenly falls. A rock burst occurs when settling earth bears down on mine walls and causes a sudden release of stored energy and exploding chunks of coal and rock.
Dave Wolny of Colorado Mesa University said small, coal-related quakes are recorded regularly in the area but this is perhaps a bit larger.
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